This week's book giveaway is in the OCAJP forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide 1Z0-808 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
To what aim? If your aim is so that a fresh image will be fetched each time because the image is changing, you can serve the image through a servlet and set the no-cache headers (as described the FAQ). If your aim is to prevent the users from saving the images to their local disk, you are out of luck. If the browser can display the image, the user can save it.